which worcester do you have now?
was it w-b that did the repair 3 months ago?
about your new boiler: yes, a COMPLETELY BY THE BOOK installed unvented system will give more flow than a large combi, about 30 lpm vs 20
but at a high cost. boiler is virtually the same price; good cylinder supply and fit at least 1500, upgrading your mains all the way from the meter, at least that again.
downside is off course with a cylinder, if you really use that high flow, you will be cold in 10 minutes or less. you will then have NO hot water at all, until the boiler finishes its next heating cycle.
a 40 kw combi will happily run 2 normal showers, if you want more, it will cost you an extra 3 grand or so